St. Mary's Hospital and Waterbury Hospital, both financially struggling, will merge into one hospital, officials announced Tuesday. Financial stability, a state-of-the-art facility and increased patient services are the goals, said the hospital officials, gathered in a conference room at Waterbury Hospital. With them were the principals of the LHP Hospital Group of Plano, Texas, which has committed $400 million to building a new hospital within four years. Officials have not yet decided where the new medical center will be. Officials said there are three possibilities -- either of the existing hospital sites or a third location yet to be determined. The new hospital will be about 750,000 square feet, or enough to accommodate about 300 inpatients and outpatients per day -- the average total number handled by both hospitals now. The two hospitals are not-for-profit, but after the merger the new medical center -- yet to be named -- will be for-profit. LHP will have 80% ownership of the venture, and each hospital will own 10%. At present, the two hospitals handle roughly the same number of inpatients, totaling about 26,000 a year.